Solder paste is typically deposited onto metallized areas on a substrate (i.e., a circuit board) by a screen printer that employs a stencil having a set of openings arranged in the same pattern as the metallized areas on the circuit board. To print paste onto the circuit board, the screen printer maintains a stencil a short distance from the circuit board such that the stencil openings are aligned with the metallized areas. Once the circuit board is in aligned registration with the stencil, a squeegee blade metal sweeps across the stencil surface to force a volume of solder paste, deposited onto the top surface of the stencil, through the stencil openings and onto the metallized areas on the circuit board
The quality of the pattern of solder paste printed onto the circuit board is dependent on several factors, including the degree to which the stencil openings remain free from obstructions. During the process of printing solder paste onto the circuit board, a small amount of solder paste often adheres to the walls of each stencil opening. Since most solder pastes contain a volatile vehicle, the paste remaining in the stencil openings tends to dry out, leaving behind a residue clogging the openings. As the stencil openings become clogged, the volume of paste deposited onto the circuit board decreases. The diminution in solder paste volume may adversely affect the quality and reliability of the solder joint with each of the metallized areas on the circuit board.
In the past, the problem of clogging of the stencil openings was addressed by removing the stencil from use and thereafter manually wiping it with a solvent-soaked rag to remove those paste residues on the stencil. There are several disadvantages to cleaning the stencil in this manner. First, such cleaning requires the intervention of an operator and may result in significant down time if the stencil must be removed from the printer. Secondly, cleaning the stencil with solvent presents environmental issues depending on the nature of the solvent.
Thus, there is a need for a technique for effecting in-situ removal of material (i.e., solder paste) from openings in a stencil without reliance on the use of solvents.